Method, system, structural member and automobile of integrated die-cast aluminum alloy

Abstract

The present disclosure relates to a preparation method and system of integrated die-casting aluminum alloy, a structural member and a vehicle, which eliminates the impurity basis of acicular phase nucleation and growth from the source by purifying the aluminum alloy raw material liquid, simultaneously adopts a high-thermal-conductivity mold for vacuum die-casting forming, and sets a cooling medium pipeline surrounding the mold cavity outside the mold cavity to deliver cooling medium to cool the mold during the forming process, effectively controls the solidification process of the aluminum alloy, greatly improves the cooling efficiency, shortens the solidification time, effectively inhibits the coarsening growth of acicular phase, and is conducive to improving the tensile strength and elongation of the integrated large die-casting aluminum alloy structural member, and is suitable for industrialization and popularization.

Description

Technical Field

[0001] This disclosure relates to a method, system, structural component, and automobile for preparing an integrated die-cast aluminum alloy. Background Technology

[0002] With the rapid development of new energy vehicles and aerospace, integrated die-casting technology, with its advantages of high efficiency, energy saving, and one-piece molding, is widely used in the production of large aluminum alloy structural parts, such as vehicle chassis, motor housings, and battery trays. The tensile strength and elongation of integrated large die-cast aluminum alloy structural parts are crucial. Summary of the Invention

[0003] This disclosure provides a method, system, structural component, and automobile for preparing an integrated die-cast aluminum alloy.

[0004] This disclosure provides a method for preparing an integrated die-cast aluminum alloy, comprising: The aluminum alloy raw material liquid is purified to obtain the purified aluminum alloy raw material liquid. The purified aluminum alloy raw material liquid is injected into a high thermal conductivity mold for vacuum die casting. The high thermal conductivity mold is made of steel with a thermal conductivity of 35~62 W / (m·K) and a tensile strength of 1200~1400 MPa. The cavity of the high thermal conductivity mold is provided with a cooling medium pipeline surrounding the cavity. During the vacuum die casting process, cooling medium is supplied to the cooling medium pipeline to cool the high thermal conductivity mold.

[0005] Optionally, the purification process includes: sequentially degassing, filtering, and settling the aluminum alloy raw material liquid.

[0006] Optionally, the degassing includes: degassing the aluminum alloy raw material liquid by rotary jetting inert gas, so that the density equivalent of the aluminum alloy raw material liquid is not higher than 2%; The filtration includes: filtering the aluminum alloy raw material liquid using a filter element to ensure that the content of oxide inclusions in the aluminum alloy raw material liquid is not higher than 0.05%; The conditions for settling include: a time of 10 to 30 minutes and a temperature of 680 to 720°C.

[0007] Optionally, by weight percentage, the steel material comprises 0.30-0.32% C, 3.0-3.7% Mo, 1.8-2.0% W, not exceeding 0.05% impurity elements, and the balance Fe, wherein the impurity elements include at least one of Ni, Cu, and Al; and / or, The inner surface of the cavity of the high thermal conductivity mold is provided with a nitriding layer and / or an antioxidant nano-coating, and the surface roughness is less than 0.8 μm.

[0008] Optionally, the cooling medium pipeline extends spirally along the outer contour of the cavity of the high thermal conductivity mold and maintains a fixed distance from the outer surface of the cavity of the high thermal conductivity mold; The distance between the cooling medium pipeline and the outer surface of the cavity of the high thermal conductivity mold is 5~8mm, the spiral arrangement spacing is 20~30mm, and the diameter of the cooling medium pipeline is 6~10mm.

[0009] Optionally, the preparation steps of the cooling medium pipeline include: The alloy powder is 3D printed according to the three-dimensional structural model corresponding to the cooling medium pipeline to obtain the printed part. The printed part is subjected to vacuum quenching, solution annealing and polishing in sequence. The alloy powder, by weight percentage, comprises 0.001-0.1% Mn, 15-22% Ni, 0.001-0.1% Cr, 4-8% Mo, 0.01-1% W, 6-10% Co, 0.5-2% Ti, no more than 0.03% impurity elements, and the balance Fe, wherein the impurity elements include P and / or S.

[0010] Optionally, the 3D printing is a laser fused deposition model, and the 3D printing conditions include: laser power of 200~300 W, scanning speed of 900~1100 mm / s, and energy density of 60~80 J / mm². 3 ; The vacuum quenching process includes: [the process is carried out under a vacuum degree not exceeding 3 × 10⁻⁶]. -3 In a vacuum environment with mbar and O2 content not exceeding 25 ppm, the sample was heated at 1400~1600℃ for 0.1~10 ms, and then cooled at a rate of 1.8×10⁻⁶ mbar. 4 Cooling under ℃ / s conditions; The solution annealing process includes: under a vacuum degree not exceeding 5 × 10⁻⁶. -3 Under a vacuum of mbar, the temperature was maintained at 800~840℃ for 1~2 hours, followed by a cooling rate of 1.8×10⁻⁶. 4 Cooled at ℃ / s, then kept at 460~485℃ for 3~7h in the same vacuum chamber, and finally cooled in air.

[0011] Optionally, the porosity of the cooling medium pipeline is less than 0.05%, and the surface hardness is greater than 1500 HV.

[0012] Optionally, it also includes: During the vacuum die casting process, the temperature of the high thermal conductivity mold is detected according to a preset detection response time, and the flow rate of the cooling medium is adjusted according to the detection results so that the average temperature of the high thermal conductivity mold is within a preset temperature range and the temperature difference does not exceed a preset temperature difference threshold.

[0013] Optionally, the preset detection response time is 1~3ms, the preset temperature range is 180~220℃, and the upper limit of the preset temperature difference threshold is 5℃; and / or, The temperature of the cooling medium is 10~25℃ and the flow rate is 2~5m / s.

[0014] Optionally, the conditions for vacuum die casting include: vacuum degree below 50 mbar, slow injection speed of 0.2~0.5 m / s, fast injection speed of 4~8 m / s, injection specific pressure of 80~120 MPa, and pressure build-up time below 20 ms.

[0015] Optionally, by weight percentage, the aluminum alloy raw material liquid includes 6.0-8.0% Si, 0.25-0.35% Mg, 0.3-0.5% Cu, 0.5-0.7% Mn, no more than 0.1% impurity elements, and the balance Al, wherein the impurity elements include at least one of Fe, Zn, and Sn.

[0016] This disclosure also provides a system for implementing the above methods, including: The purification unit is used to purify the aluminum alloy raw material liquid. The die-casting unit includes a high thermal conductivity mold, which is used to contain purified aluminum alloy raw material liquid for vacuum die-casting. The cooling unit includes a cooling medium pipeline surrounding the cavity of the high thermal conductivity mold, the cooling unit being configured to deliver a cooling medium into the cooling medium pipeline during the vacuum die casting process to cool the high thermal conductivity mold.

[0017] This disclosure also provides an integrated die-cast aluminum alloy structural component, which is prepared by the above method or the above system.

[0018] This disclosure also provides an automobile including the aforementioned integrated die-cast aluminum alloy structural component.

[0019] This disclosure eliminates the impurities that contribute to the nucleation and growth of needle-like phases by purifying the aluminum alloy raw material liquid. Simultaneously, it employs a high thermal conductivity mold for vacuum die casting and installs cooling medium pipelines surrounding the mold cavity. During the forming process, the cooling medium is delivered to cool the mold, effectively controlling the solidification process of the aluminum alloy. This significantly improves cooling efficiency and shortens solidification time, thereby effectively inhibiting the coarsening growth of needle-like phases. This is beneficial for improving the tensile strength and elongation of integrated large die-cast aluminum alloy structural parts, making it suitable for industrial application.

[0020] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0021] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings: Figure 1 This is a schematic diagram of the structure of a cooling medium pipeline according to a specific implementation method.

[0022] Figure 2 This is a schematic diagram of the cooling medium pipeline in another specific embodiment.

[0023] Figure 3 This is a microstructure photograph of the integrated die-cast aluminum alloy structural component prepared in Example 1.

[0024] Figure 4 This is a microstructure photograph of the integrated die-cast aluminum alloy structural component prepared in Comparative Example 1.

[0025] Explanation of reference numerals in the attached figures 1—High thermal conductivity mold, 2—Cooling medium pipeline. Detailed Implementation

[0026] The specific embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit this disclosure.

[0027] The microstructure of aluminum alloy castings, especially the morphology and size of the acicular phase, directly determines the mechanical properties of the castings. Coarsening of the acicular phase leads to a decrease in the tensile strength and elongation of the casting, easily causing defects such as cracks and deformation, seriously affecting the safety and lifespan of integrated die-cast parts. Related technologies for refining the acicular phase in aluminum alloys mainly fall into two categories: one is by adding refining agents (such as titanium and boron), but this method not only increases production costs but also easily leads to uneven aluminum alloy composition, thus affecting the subsequent processing performance of the casting; the other is by optimizing die-casting process parameters (such as injection pressure and pouring temperature) to improve the microstructure, but this method has a very limited effect on refining the acicular phase and is difficult to meet the stringent material performance requirements of large integrated die-cast parts.

[0028] Integrated large die-casting molds in related technologies often employ traditional water-channel designs, which suffer from low cooling efficiency, uneven cooling, and high processing difficulty. Furthermore, the mold materials have low thermal conductivity, resulting in excessively long solidification times for aluminum alloys and a tendency for acicular phases to coarsen. Simultaneously, impurities in the aluminum alloy raw material liquid can also promote the growth of acicular phases, further exacerbating performance defects in the castings.

[0029] In a first aspect, this disclosure provides a method for preparing a die-cast aluminum alloy, comprising: S1. Purify the aluminum alloy raw material liquid to obtain purified aluminum alloy raw material liquid. S2. The purified aluminum alloy raw material liquid is injected into a high thermal conductivity mold for vacuum die casting; wherein, the outer side of the cavity of the high thermal conductivity mold is provided with a cooling medium pipeline surrounding the cavity, and a cooling medium is supplied to the cooling medium pipeline during the vacuum die casting process to cool the high thermal conductivity mold.

[0030] This disclosure achieves efficient refinement of acicular phases in integrated large aluminum alloy castings through synergistic control from source purification to rapid end-stage cooling. "Integration" as used in this disclosure refers to the process of forming a complex structure, which originally required the separate manufacturing and assembly of multiple parts, into a single casting through a single die-casting process. This reduces the number of parts, connection processes, and overall weight, thereby improving structural integrity and production efficiency.

[0031] In step S1, the aluminum alloy raw material liquid is purified to remove impurities such as gases and non-metallic inclusions, thereby eliminating the matrix conditions for coarsening of the needle-like phase from the source and laying the foundation for obtaining a fine and uniform microstructure in subsequent molding.

[0032] The composition of the aluminum alloy raw material liquid is not particularly limited; for example, it can be an Al-Si-Mg series aluminum alloy raw material liquid, a 4-series aluminum alloy raw material liquid, etc. In one specific embodiment, the aluminum alloy raw material liquid is an Al-Si-Mg series heat-free high-strength aluminum alloy raw material liquid. Specifically, by weight percentage, the aluminum alloy raw material liquid may include: 6.0~8.0% Si (silicon), 0.25~0.35% Mg (magnesium), 0.3~0.5% Cu (copper), 0.5~0.7% Mn (manganese), no more than 0.1% impurity elements, and the balance Al (aluminum), wherein the impurity elements include at least one of Fe (iron), Zn (zinc), and Sn (tin).

[0033] In one specific embodiment, the purification process may include: sequentially degassing, filtering, and settling the aluminum alloy raw material liquid. Through the synergistic effect of the above steps, gases and oxide inclusions in the aluminum alloy raw material liquid can be effectively removed, ensuring the high purity and uniformity of the aluminum alloy raw material liquid.

[0034] The degassing process may include: degassing the aluminum alloy raw material liquid by rotary blowing of an inert gas, which may be argon (Ar) and / or nitrogen (N2). In practice, the inert gas can be blown into the aluminum alloy raw material liquid through a rotary nozzle, causing dissolved gases such as hydrogen to escape. This degassing process ensures that the density equivalent of the aluminum alloy raw material liquid is no higher than 2%, preferably no higher than 1.5%, which avoids the formation of pores during solidification and eliminates the unfavorable condition of hydrogen atoms and impurity elements synergistically promoting the growth of needle-like phases.

[0035] The filtration process may include filtering the aluminum alloy raw material liquid using a filter element. When the aluminum alloy raw material liquid flows through the filter element, oxide inclusions can be intercepted or adsorbed. The filter element can be made of a high-temperature resistant material. Specifically, the filter element can be one or more ceramic filter plates, and its pore size can be selected according to actual needs, for example, the pore size can be 20~40 ppi. When using multiple ceramic filter plates, filter plates with different pore sizes can be combined, for example, a combination of a ceramic filter plate with a pore size of 20 ppi and a ceramic filter plate with a pore size of 40 ppi. This filtration ensures that the oxide inclusion content of the aluminum alloy raw material liquid is no higher than 0.05%, preferably no higher than 0.03%, which significantly reduces the nucleation sites of needle-like phases, thereby inhibiting their growth. The oxide inclusions refer to oxide particles in the aluminum alloy raw material liquid, whose main components include aluminum oxide (Al2O3), magnesium oxide (MgO), and silicon oxide (SiO2).

[0036] The settling process is a crucial step in homogenizing the composition of the aluminum alloy raw material liquid and allowing for the precipitation of minute inclusions. Specifically, the settling conditions may include: a time of 10-30 minutes and a temperature of 680-720°C. These parameters maintain suitable fluidity in the aluminum alloy raw material liquid, allowing residual minute impurities to fully precipitate under gravity. Simultaneously, the composition of the aluminum alloy raw material liquid is further homogenized, providing a high-quality aluminum alloy raw material liquid for subsequent die casting.

[0037] In step S2, a high thermal conductivity mold is used instead of a traditional ordinary mold, which can quickly conduct away the latent heat released by the solidification of aluminum liquid, improving the cooling rate. At the same time, cooling medium pipelines are set around the outside of the mold cavity, allowing the cooling medium to flow close to the cavity surface, constructing a wrap-around cooling network for the cavity, effectively eliminating cooling dead zones and ensuring the uniformity of the temperature field in all parts of the mold. This efficient heat exchange process can significantly compress the solidification time of aluminum liquid, preventing solute atoms from undergoing long-range diffusion, thereby effectively inhibiting the coarsening growth of acicular phases, and ultimately obtaining die-cast aluminum alloy castings with fine grains and dense structure.

[0038] The high thermal conductivity mold is made of steel. In one specific embodiment, the thermal conductivity of the steel is 35~62 W / (m·K), preferably 50~60 W / (m·K), and the tensile strength is 1200~1400 MPa, preferably 1250~1350 MPa. Using the above-mentioned steel material to prepare the mold is beneficial to significantly improve the heat transfer efficiency, shorten the solidification time, inhibit the growth of needle-like phases, and at the same time ensure that the mold does not crack or deform during high-pressure die casting, thus ensuring process stability.

[0039] To achieve the aforementioned superior performance, the steel material may, by weight percentage, include: 0.30-0.32% C (carbon), 3.0-3.7% Mo (molybdenum), 1.8-2.0% W (tungsten), no more than 0.05% of impurity elements, and the balance Fe (iron), wherein the impurity elements include at least one of Ni (nickel), Cu (copper), and Al (aluminum).

[0040] Furthermore, to further improve the thermal fatigue life and heat transfer efficiency of the mold, and to ensure the stability of thermal conductivity and structural accuracy during die casting, the inner surface of the high thermal conductivity mold cavity can be provided with a nitriding layer and / or an anti-oxidation nano-coating. Specifically, the nitriding layer is obtained through nitriding treatment and is a nitride layer with high hardness, which is beneficial for improving wear resistance and resistance to aluminum melt erosion. The anti-oxidation nano-coating can be obtained through physical vapor deposition (PVD) process, and may include, for example, a TiAlN coating and / or an AlCrN coating, which can provide low thermal resistance and excellent anti-oxidation performance. Preferably, the anti-oxidation nano-coating can be a TiAlN-AlCrN composite coating, which can form a dense protective film on the mold surface and prevent the initiation of thermal fatigue cracks. The surface roughness (Ra) of the inner surface of the high thermal conductivity mold cavity can be below 0.8 μm, preferably below 0.5 μm, which not only helps to improve the surface finish of the casting, but also reduces the local thermal resistance caused by microscopic unevenness, allowing the heat from the aluminum melt to be transferred to the mold substrate more evenly and quickly.

[0041] In one specific implementation, such as Figure 1 As shown, the cooling medium pipeline 2 extends spirally along the outer contour of the cavity of the high thermal conductivity mold 1, advancing layer by layer in the axial direction, and maintaining a fixed distance from the outer surface of the cavity of the high thermal conductivity mold 1. The path of each loop of the pipeline roughly matches the cross-sectional contour of the cavity at that height. Thus, the cooling medium pipeline 2 can strictly follow the external geometry of the cavity to conform to its shape, effectively eliminating local temperature differences, ensuring the synchronicity of solidification of various parts of the casting, and preventing local acicular phase coarsening or hot cracking defects caused by uneven cooling. It should be understood that for cavities with complex shapes (such as structures with curved surfaces, grooves, or variable cross-sections), spiral extension means that the direction of the cooling pipeline always maintains a relatively constant distance from the cavity surface, thereby achieving enveloping cooling of the cavity.

[0042] In another implementation, such as Figure 2 As shown, the cooling medium pipeline 2 is arranged in the form of a ring around the outside of the cavity of the high thermal conductivity mold 1, and maintains a fixed distance from the outer surface of the cavity. The path of the pipeline can follow the outer contour of the cavity to form a ring channel around the cavity. For areas with irregular cross-sectional shapes of the cavity, the path of the ring pipeline can be adjusted accordingly to conform to the cavity contour, for example, by locally bending into a zigzag shape, a wavy shape, or a U-shaped bend.

[0043] In terms of specific dimensional design, the distance between the cooling medium pipeline and the outer surface of the high thermal conductivity mold cavity can be 5-8 mm. When using a spiral arrangement, the spiral spacing (i.e., the distance between two adjacent turns of the pipeline) can be 20-30 mm. This configuration is beneficial for achieving excellent cooling efficiency and effectively suppressing the growth of needle-like phases. The diameter of the cooling medium pipeline can be 6-10 mm to balance the cooling medium flow rate and fluid resistance, ensuring heat exchange efficiency. It should be understood that in practical applications, the specific routing of the cooling medium pipeline can be topologically optimized according to the hot spot distribution of the casting. For example, the spiral spacing can be increased or the pipe diameter can be enlarged in areas with concentrated hot spots to achieve targeted and precise cooling.

[0044] To achieve precise matching of the complex conformal wrapping structure of the integrated large die-cast part, the cooling medium pipeline can be fabricated using 3D printing technology. Specifically, the fabrication steps of the cooling medium pipeline may include: The alloy powder is 3D printed according to the three-dimensional structural model corresponding to the cooling medium pipeline to obtain the printed part. The printed parts are subjected to vacuum quenching, solution annealing and polishing in sequence.

[0045] The alloy powder can be selected from materials with high purity, high fluidity, and high sphericity. Specifically, by weight percentage, the alloy powder may include 0.001~0.1% Mn (manganese), 15~22% Ni (nickel), 0.001~0.1% Cr (chromium), 4~8% Mo (molybdenum), 0.01~1% W (tungsten), 6~10% Co (cobalt), 0.5~2% Ti (titanium), no more than 0.03% impurity elements, and the balance Fe. The impurity elements include P (phosphorus) and / or S (sulfur), further specifying that P ≤ 0.025% and S ≤ 0.003%. The alloy powder is a micron-sized powder, specifically, the average particle size of the alloy powder can be 15~45 μm.

[0046] The 3D printing method can be laser fused deposition modeling, which has high forming efficiency and good finished product density. Specifically, the operating conditions for 3D printing may include: substrate preheating temperature of 100~120 ℃, laser power of 200~300 W, scanning speed of 900~1100 mm / s, scanning spacing of 0.05~0.15 mm, powder feed rate of 0.03~0.07 mm, and energy density of 60~80 J / mm². 3 .

[0047] Vacuum quenching and solution annealing can eliminate residual stress from printing and improve mechanical properties. Specifically, vacuum quenching can include: [the process is described in the original text, but the provided text is incomplete and requires further context to translate accurately.] -3In a vacuum environment with mbar and O2 content not exceeding 25 ppm, the sample was heated at 1400~1600℃ for 0.1~10 ms, and then cooled at a rate of 1.8×10⁻⁶ mbar. 4 Rapid cooling at ℃ / s; solution annealing may include: under a vacuum degree not exceeding 5×10 -3 Under a vacuum of mbar, the temperature was maintained at 800~840℃ for 1~2 hours, followed by a cooling rate of 1.8×10⁻⁶. 4 Rapidly cool to room temperature at ℃ / s to obtain a fully martensitic structure, then hold at 460~485℃ for 3~7h in the same vacuum chamber, and finally cool under air conditions.

[0048] Polishing removes burrs and unmelted powder particles, ensuring a smooth inner wall of the pipeline and preventing excessive water flow resistance from affecting the cooling effect. Specifically, polishing can be performed using an abrasive flow method.

[0049] The cooling medium pipeline obtained through the above preparation steps has low porosity and high surface hardness. Specifically, its porosity can be below 0.05% and its surface hardness can be above 1500HV. It can prevent leakage under long-term scouring of the cooling medium and reduce fluid resistance, exhibiting excellent structural strength and erosion resistance.

[0050] In one embodiment, a fast-response closed-loop cooling control mechanism is established during the vacuum die casting process to avoid drastic temperature fluctuations in the mold and further improve the uniformity of the cooling rate. Specifically, the method may further include: during the vacuum die casting process, detecting the temperature of the high thermal conductivity mold according to a preset detection response time, and adjusting the flow rate of the cooling medium based on the detection results, so that the average temperature of the high thermal conductivity mold is within a preset temperature range and the temperature difference does not exceed a preset temperature difference threshold.

[0051] Specifically, the closed-loop control described above is achieved through the coordinated operation of a temperature detection module and a flow regulation module. The temperature detection module collects the cavity temperature of the high thermal conductivity mold in real time and feeds the temperature signal back to the control module. The control module outputs control commands to the flow regulation module based on the deviation between the temperature signal and the preset temperature range and temperature difference threshold. The flow regulation module adjusts the flow cross-sectional area of ​​the cooling medium pipeline according to the control commands, thereby changing the flow rate of the cooling medium. When the mold temperature is too high, the cooling medium flow rate is increased to improve the cooling rate; when the mold temperature is too low, the cooling medium flow rate is decreased to reduce the cooling rate, thus maintaining the mold temperature within the preset range. For example, the temperature detection module may include multiple temperature sensors deployed in key parts of the mold (such as hot spots or thick-walled areas), each temperature sensor collecting temperature signals at its corresponding location. The aforementioned average temperature and temperature difference are calculated based on the data collected by multiple temperature sensors. The control module may include a programmable logic controller or a temperature controller, which has built-in parameters for the preset temperature range and temperature difference threshold, and can automatically output corresponding control signals based on temperature deviations. The flow regulation module may include a flow regulation valve (such as a solenoid valve) installed on the cooling medium pipeline. By adjusting the valve opening, the flow cross-sectional area of ​​the cooling medium is changed, thereby achieving continuous or staged flow regulation. The average mold temperature refers to the arithmetic mean of the temperatures at multiple detection points on the mold cavity surface, and the temperature difference refers to the difference between the maximum and minimum temperatures at the multiple detection points.

[0052] The specific values ​​of the preset detection response time, preset temperature range, and preset temperature difference threshold can be adjusted according to actual production needs. For example, the preset detection response time can be 1~3ms, the preset temperature range can be 180~220℃, and the upper limit of the preset temperature difference threshold can be 5℃. Furthermore, the temperature and flow rate of the cooling medium can be adjusted within a certain range; specifically, the temperature of the cooling medium can be 10~25℃, and the flow rate can be 2~5m / s, to obtain the desired heat exchange efficiency. Millisecond-level response speed and precise temperature and flow rate control facilitate rapid intervention in the mold's thermal balance, ensuring that the aluminum alloy solidifies rapidly at the optimal cooling rate (e.g., 15~25℃ / s) (solidification time, e.g., 10~20s), further improving the refinement effect of the acicular phase. The cooling medium can be a common liquid coolant; for example, the cooling medium can include pure water, industrial circulating cooling water, etc.

[0053] The vacuum die casting process includes pouring, injection filling, pressurization and shrinkage compensation, and solidification and cooling stages. In the pouring stage, the pouring temperature of the aluminum alloy molten material can be controlled at 680~720℃ before being injected into the mold cavity. After the aluminum alloy molten material is injected into the cavity, the injection process is divided into a slow injection stage and a fast injection stage. The slow injection speed can be 0.2~0.5 m / s, and the fast injection speed can be 4~8 m / s. After the cavity is filled, the pressurization and shrinkage compensation stage begins, with a pressure build-up time of less than 20 ms and an injection specific pressure of 80~120 MPa. During filling and compaction, the vacuum degree within the cavity can be maintained below 50 mbar. With the synergistic cooling effect of the high thermal conductivity mold and cooling medium pipeline, the solidification time of the aluminum alloy molten material can be significantly shortened, for example, controlled to 10~20 s, achieving efficient refinement of the acicular phase. After die casting, spray cooling can be used to cool the casting, and the demolding temperature can be controlled to not exceed 200℃ to avoid hot cracking defects.

[0054] The method disclosed herein is simple and controllable, provides stable refining effect on acicular phases, reduces the use of refining agents, avoids compositional inhomogeneity, effectively improves the mechanical properties and yield of aluminum alloy castings, increases die-casting production efficiency, reduces mold wear and production costs, can be directly adapted to existing integrated large die-casting production lines, has low modification difficulty and strong replicability, and is suitable for industrial promotion.

[0055] A second aspect of this disclosure provides a system for carrying out the above-described method for preparing die-cast aluminum alloys, the system comprising: The purification unit is used to purify the aluminum alloy raw material liquid. The die-casting unit includes a high thermal conductivity mold, which is used to contain purified aluminum alloy raw material liquid for vacuum die-casting. The cooling unit includes a cooling medium pipeline surrounding the cavity of the high thermal conductivity mold, the cooling unit being configured to deliver a cooling medium into the cooling medium pipeline during the vacuum die casting process to cool the high thermal conductivity mold.

[0056] The collaborative relationships between the units are consistent with those described in the above method embodiments, and will not be repeated here.

[0057] This disclosure also provides a die-cast aluminum alloy structural component, which is prepared by the above method or by the above system.

[0058] This structural component possesses a fine and uniform microstructure and excellent mechanical properties, meeting the stringent material performance requirements of integrated large die-cast parts. Specifically, the average length of the acicular phase (such as iron-rich phase or eutectic silicon) in this structural component does not exceed 20 μm, preferably 8~18 μm, and is uniformly distributed without obvious coarse dendrites or agglomeration; its tensile strength is not less than 260 MPa, preferably 275~295 MPa, and its elongation is not less than 9%, preferably 10~15%.

[0059] The structural components described are particularly suitable for key structural components of new energy vehicles, such as the vehicle chassis, rear floor, battery tray, or sill beam. They can not only effectively reduce vehicle weight and improve energy efficiency, but also absorb impact energy through good plastic deformation in the event of a collision, thus ensuring passenger safety.

[0060] This disclosure also provides an automobile including the aforementioned die-cast aluminum alloy structural component.

[0061] There are no restrictions on the specific type and structure of the vehicle. For example, it can be a new energy vehicle. By applying the above-mentioned high-performance die-cast aluminum alloy structural components, the vehicle body achieves lightweighting while ensuring the safety and reliability of the structure.

[0062] The technical solutions of this disclosure are further described in detail below with reference to specific embodiments and comparative examples, but are not intended to limit this disclosure.

[0063] In the following embodiments, the microstructure photographs of the castings were taken using a metallographic microscope.

[0064] Example 1 Integrated die-cast aluminum alloy structural parts are prepared using the method described in this disclosure. An Al-Si-Mg series heat-treatable high-strength aluminum alloy is selected as the raw material, with the following composition: 6.9% Si, 0.3% Mg, 0.4% Cu, 0.68% Mn, ≤0.05% other impurities (Zn / Sn), and the balance Al. The high thermal conductivity mold is prepared using mold steel with a thermal conductivity of 59 W / (m·K) and a tensile strength of 1350 MPa, with the following composition: 0.3% C, 3.1% Mo, 1.85% W, ≤0.05% impurities (Ni / Cu), and the balance Fe. The inner surface of the mold cavity is coated with a nitrided layer and a TiAlN-AlCrN composite anti-oxidation nano-coating, with a surface roughness Ra of 0.5 μm. Cooling medium pipelines were 3D printed using laser fused deposition modeling (FLDM). The alloy powder composition was: 0.009% Mn, 17.6% Ni, 0.009% Cr, 6% Mo, 0.01% W, 8% Co, 1.5% Ti, with the balance being Fe and ≤0.01% impurity elements, including 0.008% P and 0.001% S. The substrate was preheated to 110 °C, the laser power was 250 W, the scanning speed was 1000 mm / s, the scanning spacing was 0.10 mm, the powder feed rate was 0.05 mm, and the energy density was 78 J / mm². 3 Interlayer cooling time ≤ 0.1s / layer, printed parts are vacuum quenched (vacuum degree 3×10). -3 mbar, O2 content not exceeding 25ppm, heating at 1500℃ for 5ms, cooling rate 1.8×10 4 ℃ / s), solution annealing (vacuum degree ≤5×10 -3 The material was heated to 820℃ for 1.5 hours, then rapidly cooled to room temperature under vacuum to obtain a fully martensitic structure. After being held at 480℃ for 5 hours in the same vacuum chamber (followed by air cooling) and then polished with abrasive flow, the porosity was 0.03%, and the inner wall surface hardness was 1580 HV. The cooling medium pipeline extended spirally along the outer contour of the mold cavity, with a distance of 6 mm between the pipeline and the outer surface of the cavity, a spiral spacing of 25 mm, and a pipeline diameter of 8 mm. The specific steps are as follows: (1) Purification treatment: The aluminum alloy raw material liquid was subjected to rotary argon degassing, filtration with a ceramic filter plate with a pore size of 30ppi and settling (690℃, 20min) in sequence to obtain the purified aluminum alloy raw material liquid with a density equivalent of 1.5% and an oxide inclusion content of 0.03% by weight.

[0065] (2) Vacuum die casting: The purified aluminum alloy raw material liquid is injected into the mold at a pouring temperature of 700℃. The slow injection speed is 0.3m / s, the fast injection speed is 6m / s, the injection specific pressure is 100MPa, the pressure build-up time is 15ms, and the cavity vacuum degree is 30mbar. During the die casting process, the mold temperature is monitored in real time by a temperature sensor (detection response time 2ms) and the flow rate of the cooling medium is adjusted. The average mold temperature is controlled at 195℃ with a temperature difference of 3℃. The cooling medium is 15℃ deionized water with a flow rate of 3m / s and a solidification time of 15s. After molding, an integrated die-cast aluminum alloy structural part is obtained.

[0066] Microscopic photographs of the structural component are as follows: Figure 3 As shown, the needle-like phases are uniformly distributed and small in size, and no obvious areas of coarse needle-like phase aggregation were observed.

[0067] Comparative Example 1 The difference from Example 1 is that a traditional straight-hole cooling water channel is used instead of a spiral-extended cooling medium pipeline. The straight-hole cooling water channel consists of equally spaced parallel straight holes arranged along the length of the mold, with a channel diameter of 8 mm and a spacing of 25 mm. All other conditions are the same as in Example 1.

[0068] Microscopic photographs of the structural component are as follows: Figure 4 As shown, the needle-like phase is relatively large, and there are areas of coarsening and aggregation of the needle-like phase, with an overall uneven distribution.

[0069] Comparative Example 2 The difference from Example 1 is that a mold made of conventional hot work die steel (thermal conductivity 25 W / (m·K), tensile strength 1150 MPa) is used instead of a high thermal conductivity mold. All other conditions are the same as in Example 1.

[0070] Comparative Example 3 The difference from Example 1 is that the aluminum alloy molten material is not purified and is directly injected into the mold at a pouring temperature of 700°C. All other conditions are the same as in Example 1.

[0071] Test case The die-cast parts of the examples and comparative examples were tested as follows, and the results are listed in Table 1.

[0072] Average length of acicular phase: determined using metallographic microscopy combined with image analysis. After the sample was polished with 400x and 1000x sandpaper, it was photographed under a metallographic microscope at no less than 5 fields of view. The length of the acicular phase was statistically analyzed using image analysis software, and the arithmetic mean was calculated as the average length of the acicular phase.

[0073] Tensile strength and elongation: Standard tensile specimens were prepared according to the national standard GB / T 228.1-2021 "Metallic materials - Tensile testing - Part 1: Test method at room temperature". The tensile test was carried out at room temperature on an electronic universal testing machine with a tensile rate of 2 mm / min. The tensile strength Rm and elongation after fracture A were measured.

[0074] Table 1

[0075] As shown in Table 1, the integrated die-cast aluminum alloy structural component prepared in Example 1 achieved excellent acicular phase refinement, and both tensile strength and elongation were significantly improved.

[0076] The preferred embodiments of this disclosure have been described in detail above with reference to the accompanying drawings. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0077] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0078] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A method for preparing an integrated die-cast aluminum alloy, characterized in that, include: The aluminum alloy raw material liquid is purified to obtain the purified aluminum alloy raw material liquid. The purified aluminum alloy raw material liquid is injected into a high thermal conductivity mold for vacuum die casting. The high thermal conductivity mold is made of steel with a thermal conductivity of 35-62 W / (m·K) and a tensile strength of 1200-1400 MPa. By weight percentage, the steel includes 0.30-0.32% C, 3.0-3.7% Mo, 1.8-2.0% W, no more than 0.05% impurity elements, and the balance Fe. The impurity elements include at least one of Ni, Cu, and Al. A ring is provided on the outer side of the cavity of the high thermal conductivity mold. A cooling medium pipeline surrounds the cavity, into which cooling medium is supplied during the vacuum die casting process to cool the high thermal conductivity mold. The cooling medium pipeline is prepared by 3D printing from alloy powder, which, by weight percentage, comprises 0.001~0.1% Mn, 15~22% Ni, 0.001~0.1% Cr, 4~8% Mo, 0.01~1% W, 6~10% Co, 0.5~2% Ti, no more than 0.03% impurity elements, and the balance Fe, wherein the impurity elements include P and / or S.

2. The method according to claim 1, characterized in that, The purification process includes: sequentially degassing, filtering, and settling the aluminum alloy raw material liquid.

3. The method according to claim 2, characterized in that, The degassing process includes: degassing the aluminum alloy raw material liquid by rotating and blowing inert gas to ensure that the density equivalent of the aluminum alloy raw material liquid is not higher than 2%; The filtration includes: filtering the aluminum alloy raw material liquid using a filter element to ensure that the content of oxide inclusions in the aluminum alloy raw material liquid is not higher than 0.05%; The conditions for settling include: a time of 10 to 30 minutes and a temperature of 680 to 720°C.

4. The method according to claim 1, characterized in that, The inner surface of the cavity of the high thermal conductivity mold is provided with a nitriding layer and / or an antioxidant nano-coating, and the surface roughness is less than 0.8 μm.

5. The method according to claim 1, characterized in that, The cooling medium pipeline extends spirally along the outer contour of the cavity of the high thermal conductivity mold and maintains a fixed distance from the outer surface of the cavity of the high thermal conductivity mold. The distance between the cooling medium pipeline and the outer surface of the cavity of the high thermal conductivity mold is 5~8mm, the spiral arrangement spacing is 20~30mm, and the diameter of the cooling medium pipeline is 6~10mm.

6. The method according to claim 1, characterized in that, The preparation steps of the cooling medium pipeline include: The alloy powder is 3D printed according to the three-dimensional structural model corresponding to the cooling medium pipeline to obtain the printed part. The printed part is subjected to vacuum quenching, solution annealing and polishing in sequence. The porosity of the cooling medium pipeline is less than 0.05%, and the surface hardness is greater than 1500HV.

7. The method according to claim 6, characterized in that, The 3D printing method is laser fused deposition modeling, and the printing conditions include: laser power of 200-300 W, scanning speed of 900-1100 mm / s, and energy density of 60-80 J / mm². 3 ; The vacuum quenching process includes: [the process is carried out under a vacuum degree not exceeding 3 × 10⁻⁶]. -3 In a vacuum environment with mbar and O2 content not exceeding 25 ppm, the sample was heated at 1400~1600℃ for 0.1~10 ms, and then cooled at a rate of 1.8×10⁻⁶ mbar. 4 Cooling under ℃ / s conditions; The solution annealing process includes: under a vacuum degree not exceeding 5 × 10⁻⁶. -3 Under a vacuum of mbar, the temperature was maintained at 800~840℃ for 1~2 hours, followed by a cooling rate of 1.8×10⁻⁶. 4 Cool to room temperature at ℃ / s, then hold at 460~485℃ for 3~7h in the same vacuum chamber, and finally cool under air conditions.

8. The method according to claim 1, characterized in that, Also includes: During the vacuum die casting process, the temperature of the high thermal conductivity mold is detected according to a preset detection response time, and the flow rate of the cooling medium is adjusted according to the detection results so that the average temperature of the high thermal conductivity mold is within a preset temperature range and the temperature difference does not exceed a preset temperature difference threshold.

9. The method according to claim 8, characterized in that, The preset detection response time is 1~3ms, the preset temperature range is 180~220℃, and the upper limit of the preset temperature difference threshold is 5℃; and / or, The temperature of the cooling medium is 10~25℃ and the flow rate is 2~5m / s.

10. The method according to claim 1, characterized in that, The conditions for vacuum die casting include: vacuum degree below 50 mbar, slow injection speed of 0.2~0.5 m / s, fast injection speed of 4~8 m / s, injection specific pressure of 80~120 MPa, and pressure build-up time below 20 ms.

11. The method according to claim 1, characterized in that, The aluminum alloy raw material liquid comprises, by weight percentage, 6.0-8.0% Si, 0.25-0.35% Mg, 0.3-0.5% Cu, 0.5-0.7% Mn, no more than 0.1% impurity elements, and the balance Al, wherein the impurity elements include at least one of Fe, Zn, and Sn.

12. A system for implementing the method according to any one of claims 1 to 11, characterized in that, include: The purification unit is used to purify the aluminum alloy raw material liquid. The die-casting unit includes a high thermal conductivity mold, which is used to contain purified aluminum alloy raw material liquid for vacuum die-casting. The cooling unit includes a cooling medium pipeline surrounding the cavity of the high thermal conductivity mold, the cooling unit being configured to deliver a cooling medium into the cooling medium pipeline during the vacuum die casting process to cool the high thermal conductivity mold.

13. An integrated die-cast aluminum alloy structural component, characterized in that, It is prepared by the method according to any one of claims 1 to 11 or by the system according to claim 12.

14. A car, characterized in that, Includes the integrated die-cast aluminum alloy structural component as described in claim 13.

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